Solution Chemistry, Substrate, and Processing Effects on Chemical Homogeneity in Lead Zirconate Titanate Thin Films

The effects of chemistry, substrate, and processing conditions on through-thickness cation distributions are explored in solution-derived morphotropic composition lead zirconate titanate (PZT) films. Films prepared from chelate-based and conventional sol-gel chemistries were spin cast onto Pt/ZnO/SiO<inf>2</inf>/Si and Pt/Ti/SiO<inf>2</inf>/Si substrates and pyrolyzed at 300°C, 350°C, and 400°C prior to crystallization at 700°C either in a preheated furnace or via rapid thermal processing. For films crystallized within a conventional furnace on Pt/ZnO/SiO<inf>2</inf>/Si substrates no chemical gradients were observed. All films prepared on Pt/Ti/SiO<inf>2</inf>/Si substrates had increased titanium concentrations near the PZT/Pt interfaces, and the source is shown to be titanium diffusing from the substrate metallization stack. The effect of heating method and rate was explored in films prepared on Pt/ZnO/SiO<inf>2</inf>/Si substrates with 15°C, 50°C, and 100°C/s heating rates within a rapid thermal annealer. Only one solution chemistry-heating rate combination resulted in the formation of a chemical gradient: a conventional sol-gel chemistry and a 50°C/s heating rate. Infrared spectroscopy of pyrolyzed gel films showed absorption spectra differences in the bonding structure between the two chemistries with the conventional sol-gel-derived films exhibiting a signature more similar to that of a PbTiO<inf>3</inf> gel, suggestive of a gel-structure source of gradient formation during crystallization.